psignal and psiginfo should not be exposed in environments prior to POSIX 2008
This issue grew out of work to make these functions compliant with POSIX 2008 (Issue #5863). According to Garrett, siginfo.h needs to be wrapped in
#if defined(_XPG7) || !defined(_STRICT_SYMBOLS) ... #endif
so that they are properly suppressed in environments prior to POSIX 2008/SUSv4.